The present invention generally relates to fuel-fired heating appliances and, in a preferred embodiment thereof, more particularly provides a gas-fired water heater having a combustion chamber bottom wall portion defined by a perforated flame arrestor plate with which an overlying scale deflector shield structure is operatively associated.
Gas-fired residential and commercial water heaters are generally is formed to include a vertical cylindrical water storage tank with a gas burner structure disposed in a combustion chamber below the tank. The burner is supplied with a fuel gas through a gas supply line, and combustion air through one or more air inlet passages providing communication between ambient air and the interior of the combustion chamber.
Water heaters of this general type are extremely safe in operation. However, when gasoline or other flammable liquids are stored or used improperly in proximity to the water heater, there may exist a possibility of flammable vapors becoming entrained in the air intake of the water heater. It is theorized that such vapors might cause secondary combustion to occur within the confines of the water heater combustion chamber. It is accordingly possible for the resulting flame to propagate out of the combustion chamber into the ambient environment around the water heater as a result of following the intake path of the flammable vapor.
In view of this, various modern gas-fired water heater designs, as well as the designs of other types of fuel-fired heating appliances, focus upon the inhibition and/or control of the entrance of flammable vapors into the combustion chamber of the appliance. One previously proposed method of carrying out this design goal is to provide the combustion chamber with a bottom wall portion defined by a flame arrestor plate structure in which a spaced series of flame quenching combustion air inlet openings are formed.
During firing of the water heater, combustion air is drawn upwardly through these openings into the combustion chamber, mixed with fuel being discharged from the burner, and combusted to create heat transferred to water stored in the tank portion of the water heater. The combustion air inlet openings are configured in a manner such that they readily permit combustion air, and extraneous flammable vapors entrained therein, to pass therethrough into the combustion chamber, while at the same time substantially precluding downward passage of combustion chamber flames through the openings.
In order to perform their flame quenching function, these openings are typically quite small, and may be susceptible to clogging by particulate matter. Such clogging undesirably reduces the overall combustion efficiency of the water heater. Among the sources of particulate matter, which can restrict combustion air inlets, are the eventual creation of scale deposits normally generated as the gas-side surfaces of the water tank degrade with oxidation of the metal surfaces that are exposed to combustion gases. Over time, some of these scale deposits tend to flake off the gas-side surfaces of the bottom head and flue walls, thereby falling onto the top side of the arrestor plate and eventually clogging some of the arrestor plate openings.
It would be desirable to provide an arrestor plate structure for the combustion chamber of a fuel-fired heating appliance, such as a gas-fired water heater, which eliminates or at least substantially reduces this potential air inlet clogging problem. It is to this goal that the present invention is primarily directed.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, specially designed fuel-fired heating apparatus is provided which is representatively in the form of a gas-fired water heater, but could alternatively be fuel-fired heating apparatus of another type such as, for example, a fuel-fired boiler or furnace.
From a broad perspective, the fuel-fired heating apparatus comprises a combustion chamber communicatable with a fluid to be heated and having vertically spaced apart, facing top and bottom wall structures, a portion of the bottom wall structure having combustion air inlet openings therein which are preferably configured and operative as flame quenching openings. Representatively, such bottom wall structure is defined by a perforated flame arrestor plate having a plate-like body in which the flame quenching combustion air inlet openings are suitably formed. A fuel burner is disposed within the combustion chamber and is supplied with fuel via a fuel supply pipe connected thereto and extending through the combustion chamber.
The fuel-fired heating apparatus further comprises a shield member disposed within the combustion chamber, overlying the combustion air inlet openings in an upwardly spaced relationship therewith, and positioned to intercept particulate matter, such as scale, falling from the top combustion chamber wall structure to prevent the fallen particulate matter from landing in and clogging the combustion air inlet openings. Representatively, the shield member has an upwardly domed configuration and has a peripheral portion which is suitable secured to a peripheral portion of the arrestor plate body.
In one illustrated embodiment of the fuel-fired heating apparatus, the mutually spaced series of combustion air inlet openings are distributed over substantially all of the arrestor plate body, and the shield member extends across substantially the entire top side of the arrestor plate, in an upwardly spaced relationship therewith, and has a top side cutout area receiving the fuel burner and a portion of the fuel supply pipe. The shield member defines a combustion air receiving plenum, disposed above the flame arrestor plate within the combustion chamber, which is operative to receive combustion air upwardly exiting the combustion air inlet openings, the combustion air receiving plenum communicating with the balance of the combustion chamber through such cutout area.
In another illustrated embodiment of the fuel-fired heating apparatus, the mutually spaced series of air inlet openings are disposed in only a part of the arrestor plate body, with the balance of the body being substantially imperforate. The shield member extends across the top side of only the perforated part of the arrestor plate body, in an upwardly spaced relationship therewith, and defines a combustion air receiving plenum, disposed within the combustion chamber above the combustion air inlet openings, which is operative to receive combustion air upwardly exiting the combustion air inlet openings, the combustion air receiving plenum having an outlet portion through which it communicates with the balance of the combustion chamber. Representatively, such outlet portion is defined by an outlet opening which faces in a direction parallel to the top side of the arrestor plate body.
In an illustrated fuel-fired water heater embodiment of the invention, a flue extends upwardly from the top wall structure and through water stored in a tank portion of the water heater. The shield member is operative to prevent particulate matter, such as scale, from falling from the flue and/or the top combustion chamber wall and landing in and clogging the air inlet openings.